1. Field of the Invention
The present invention relates generally to radio frequency identification (RFID), and more particularly to methods, systems and apparatus for writing data to RFID tags.
2. Background
Radio frequency identification (RFID) systems generally include at least one interrogator (reader) that communicates with at least one RFID tag using radio frequency (RF) signals. Each tag stores data that may include common information and unique identification (ID) information. A tag may be associated with a single item or unit of items (e.g., a skid, box, cargo container, truck, or the like), where the RFID tag data provides information about the item or unit of items. A tag may also be associated with an individual or an animal. An interrogator (reader) communicates with one or a plurality of RFID tags to read RFID tag data or a portion of the tag data, or to write data to a tag. In this manner, it is possible to non-invasively perform various functions, such as identifying, detecting, sorting and tracking an item, monitoring inventory, preventing sale of out-of-date or potentially damaged stock, preventing unauthorized entry, exit or removal from a warehouse, store or other designated location, and the like.
The process of writing data to RFID tags follows a specific sequence. For example, in the Class 1, Generation 2 (Gen-2) standard, an interrogator issues a Write command and then transmits a continuous wave (CW) signal for a predefined time period (e.g., either 20 ms or the time between the Write command and the tag's backscattered reply). A tag may reply with an acknowledgement that the write completely successfully or an error code. If the interrogator does not receive a reply within a predefined period (e.g., 20 ms), the interrogator may reissue the Write command. Current Gen-2 tag designs effectively “drop out” and ignore further commands during the CW portion of the Write sequence.
The Write sequence described above has several performance limitations, particularly when writing data to a large population of tags. Passive RFID tags utilizing the EPC Global Gen2 standard typically require up to 20 mS per word written in order to perform a store operation into non-volatile memory before reporting status to the Interrogator. As discussed above, the interrogator waits for a response to the issued Write command that includes status information relevant to the write operation before transmitting the next command. For large groups of tags, this process becomes time consuming because of the time required to process the Write command at each tag, particularly compared to the time required to actually transmit the command. This presents a performance bottleneck for some applications writing data to a large population of tags. These applications could benefit from a faster overall write access time.
What is needed are methods and systems for increasing the performance of write operations, particularly to large tag populations.
Exemplary embodiments of the present invention will be described with reference to the accompanying drawings, wherein like numbers designate like or similar elements or features, and like numbers having different lower case letters represent corresponding elements/features. The drawing in which an element first appears typically is indicated by the leftmost digit in the corresponding reference number.